Molding is a process by virtue of which a molded article can be formed from molding material (such as Polyethylene Teraphalate (PET), Polypropylene (PP) and the like) by using a molding system. Various molded articles can be formed by using the molding process, such as an injection molding process. One example of a molded article that can be formed, for example, from PET material is a preform that is capable of being subsequently blown into a beverage container, such as, a bottle and the like.
As an illustration, injection molding of PET material typically involves heating the PET material to a homogeneous molten state and injecting, under pressure, the so-melted PET material is injected into a molding cavity defined, at least in part, by a female cavity piece and a male core piece mounted respectively on a cavity plate and a core plate of the mold. The cavity plate and the core plate are urged together and are held together by clamp force, the clamp force being sufficient enough to keep the cavity and the core pieces together against the pressure of the injected PET material. The molding cavity has a shape that substantially corresponds to a final cold-state shape of the molded article to be molded. The so-injected PET material is then cooled to a temperature sufficient to enable ejection of the so-formed molded article from the mold. When cooled, the molded article shrinks inside of the molding cavity and, as such, when the cavity and core plates are urged apart, the molded article tends to remain associated with the core piece. Accordingly, by urging the core plate away from the cavity plate, the molded article can be de-molded, i.e. ejected off of the core piece. Ejection structures are known to assist in removing the molded articles from the core halves. Examples of the ejection structures include stripper plates, stripper rings and neck rings, ejector pins, etc.
When dealing with molding a preform that is capable of being blown into a beverage container, one consideration that needs to be addressed is forming a so-called “neck region”. Typically and as an example, the neck region includes (i) threads (or other suitable structure) for accepting and retaining a closure assembly (ex. a bottle cap), and (ii) an anti-pilferage assembly to cooperate, for example, with the closure assembly to indicate whether the end product (i.e. the beverage container that has been filled with a beverage and shipped to a store) has been tampered with in any way. The neck region may comprise other additional elements used for various purposes, for example, to cooperate with parts of the molding system (ex. a support ledge, etc.). As is appreciated in the art, the neck region can not be easily formed by using the cavity and core halves. Traditionally, split mold inserts (sometimes referred to by those skilled in the art as “neck rings”) have been used to form the neck region.
With reference to FIG. 1, a section along a portion of an injection mold 10 illustrates a portion of typical mold stack 16 that is arranged within a molding system (not depicted). The description of FIG. 1 that will be presented herein below will be greatly simplified, as it is expected that one skilled in the art will appreciate configuration of other components of the injection mold 10.
The mold stack 16 includes a first stack portion 17 and a second stack portion 18 that are associated, in use, with a first mold half 14 and a second mold half 12 of the injection mold 10, respectively. The first stack portion 17 and the second stack portion 18 are arrangeable, in use, to define a molding cavity 19 therebetween within which molding material may be injected to form a molded article. The first stack portion 17 includes a core insert 20, a lock ring 30, and a neck ring pair 40. The core 20 and the neck ring pair 40 each include molding surfaces with which to define an inner body portion and an encapsulated portion (e.g. for molding the neck region on the preform/container) of the molding cavity 19, respectively. The lock ring 30 does not define any portion of the molding cavity 19, although this is not always so, and wherein the lock ring 30 is provided to both retain the core insert 20 to a core plate (not shown) and to align and hold closed (i.e. keep the halves thereof in a closed configuration) the neck ring pair 40 during a step of molding of the molded article. The second stack portion 18 includes a cavity insert 50 and a gate insert 60 with which to define an outer body portion and a gate portion of the molding cavity 19. The gate insert 60 is further configured to connect the molding cavity 19 to a melt distribution system (not shown). Lastly, and much like the lock ring 30, the cavity insert 50 is also configured to both align and hold closed the neck ring pair 40 during the step of molding.
Also shown are a slide pair 70 upon which the neck ring pair 40 are mounted. The slide pair 70 is slidably mounted on a top surface of a stripper assembly 72. As commonly known, and as generally described in U.S. Pat. No. 6,799,962 to Mai et al (granted on Oct. 5, 2004), the stripper assembly 72 is configured to be movable relative to a cavity plate assembly 74 and a core plate assembly (not depicted), when the mold in arranged in an open configuration, whereby the slide pair 70, and the complementary neck ring insert pair 40 mounted thereon, can be laterally driven, via a cam arrangement (not shown), for the release of the molded article from the molding cavity 19.
The neck ring 40 has a body that includes a first projecting portion 45 and a second projecting portion 46 that extend from a top and a bottom face of a flange portion 48. As shown, the first projecting portion 45 and the second projecting portion 46 may be structured in the form of male tapers.
In operation, with the mold stack 16 being closed, as shown, to define the molding cavity 19, the first projecting portion 45 and the second projecting portion 46 are arranged to cooperate with a first seat 52 and a second seat 32 that are defined in the cavity insert 50 and the lock ring 30 to both align and lock the neck ring pair 40 in relation thereto. As shown, the first seat 52 and the second seat 32 may be structured in the form of female tapers.
Also shown, is a parting line 26 between the molding surfaces of the core insert 20 and the neck ring 40 (i.e. the place where the molding surfaces of the neck ring pair 40 and core insert 20 meet) that is pushed up inside the neck ring pair 40. More particularly, the parting line 26 is located at an interface between top face of a protuberance 22 that is defined around a medial portion of the core insert 20 and a recessed face of a pocket 42 that is defined through the bottom face of the neck ring pair 40. Also note that an inner annular portion of the top face of the protuberance 22 defines molding surface with which to define a top end portion of the molding cavity 19 (e.g. for molding a top sealing surface of the neck region on the container). A technical effect of the foregoing may include flexibility of parting line location for sake of molding neck regions having shorter threads with lower risk of ejection related issues. Furthermore, by moving the parting line 26 to be in line with the flange 48 of the neck ring pair 40, which may be cooled by means (not shown) of a coolant circulating therethrough, certain cooling related defects (e.g. parting line indentation) may be avoided.
A description of a mold stack that is similar to the foregoing may be referenced in US Patent Application US2009/0214694 to Mai, published on Aug. 27, 2009, which discloses, amongst other things, a mold insert stack for use in an injection mold and a coupler thereof.
The mold insert stack for use in an injection mold is provided and comprises a core assembly that includes: a core insert that includes: a core body; an inner molding surface that is defined on the core body, the inner molding surface provides, in use, an inner portion of a molding cavity that is shaped to mold a preform; a core-coupler interface that is defined on the core body; a support member that includes: a support body; a support-sliding interface that is defined on the support body; a coupler member that includes: a coupler body; a coupler-core interface that is defined on the coupler body; a coupler-insert interface that is defined on the coupler body; and a complementary sliding interface that is defined on at least one of the coupler body and the core body; the coupler-core interface and the core-coupler interface being configured to cooperate, in use, to mutually locate the coupler body with the core body; the coupler-insert interface being configured to cooperate, in use, with a complementary interface defined on a further mold insert; the support-sliding interface and the complementary sliding interface being configured to cooperate, in use, to establish a slidable coupling that is able to accommodate, in use, a lateral move between the support-sliding interface and the complementary sliding interface and connect a load path between the support body with at least one of the core body with the coupler body.